1. Polygenetic inheritance

2. Polygenetic inheritance
Objectives
Outline what polygenetic inheritance is.
Outcomes
3: Describe an example of polygenetic inheritance.
5: Explain why polygenetic inheritance arises.
7: Evaluate the importance of polygenetic characteristics in variation and evolution.
Key terms: polygenetic inheritance, continuous, variation.

3. 10.3.1 Define Polygenic inheritance
Polygenic Inheritance – When a single trait is influenced by many genes.
Each allele of a polygenic character often contributes only a small amount to the over all phenotype.
This makes studying the individual alleles difficult.
In addition environmental effects smooth out the genotypic variation to give continuous distribution curves.
Occurs when there are more than one
gene that controls the phenotype.
• The more chromosomes involved
contributes to more variation.
• Human skin color seems to be controlled
by three or four chromosomes.
• Human hair color is also controlled by
various genes.

5. Skin colour video

7. Polygenetic inheritance
Outcomes
3: Describe an example of polygenetic inheritance.
5: Explain why polygenetic inheritance arises.
7: Evaluate the importance of polygenetic characteristics in variation and evolution.
Key terms: polygenetic inheritance, continuous, variation.

8. Polygenetic inheritance
Outcomes
3: Describe an example of polygenetic inheritance.
5: Explain why polygenetic inheritance arises.
7: Evaluate the importance of polygenetic characteristics in variation and evolution.
Key terms: polygenetic inheritance, continuous, variation.

9. Polygenetic inheritance
Outcomes
3: Describe an example of polygenetic inheritance.
5: Explain why polygenetic inheritance arises.
7: Evaluate the importance of polygenetic characteristics in variation and evolution.
Key terms: polygenetic inheritance, continuous, variation.

10. Polygenetic inheritance
Outcomes
3: Describe an example of polygenetic inheritance.
5: Explain why polygenetic inheritance arises.
7: Evaluate the importance of polygenetic characteristics in variation and evolution.
Key terms: polygenetic inheritance, continuous, variation.

11. Polygenetic inheritance
Outcomes
3: Describe an example of polygenetic inheritance.
5: Explain why polygenetic inheritance arises.
7: Evaluate the importance of polygenetic characteristics in variation and evolution.
Key terms: polygenetic inheritance, continuous, variation.

12. Polygenic Inheritance of skin color
At least four loci and possibly more genes are involved.
Example 3 loci: each has two possible alleles: A,a B,b C,c,
each capital allele adds one unit of darkness
each lower case allele adds nothing
Parents with
intermediate tone
aabbcc
AABBCC
Offspring can have tone darker or lighter than either parent

13. Polygenic Inheritance of skin color
Most examples of polygenic inheritance involve more than two genes with codominant alleles. As the number of genes involved increases, the number of posible phenotypes increases. Eventually, it becomes impossible to divide individuals into discrete groups-the variation is continuous. 1 2 3 4 5 6
Number of ‘darker’ alleles

21. Key terms: polygenetic inheritance, continuous, variation.
Questions
1. Which human trait shows a pattern of polygenetic inheritance?
A. ABO blood type
B. Sickle cell anaemia
C. Skin colour
Co-dominant alleles
2. Why is it sometimes difficult to identify how certain characteristics are inherited in humans.
A. Most genes are linked.
B. Rates of mutation are high.
C. The inheritance may be polygenic.
The environment varies so little.
3. Describe the effects of polygenic inheritance using two specific examples. (5)
Key terms: polygenetic inheritance, continuous, variation.

22. Key terms: polygenetic inheritance, continuous, variation.
Questions C
3. More than one gene controls / affects one characteristic;
Reject more than 2 alleles
can cause continuous variation / many different possible phenotypes;
eg skin colour / other valid example;
allele of each gene promotes melanin production or not / other valid example;
eg grain colour in wheat / other valid example;
allele of each gene promotes pigment production or not / other valid example; 5 max
If first or second example is incorrect do not accept third or subsequent examples.
Key terms: polygenetic inheritance, continuous, variation.